Short-term response of benthic foraminifera to fine sediment depositional events simulated in microcosm

Guilhermic, Corentin; Nardelli, Maria Pia; Mouret, Aurélia; Le Moigne, Damien; Howa, Hélène

doi:https://doi.org/10.5194/bg-2023-31

Preprints

https://doi.org/10.5194/bg-2023-31

Preprints

20 Feb 2023

| 20 Feb 2023

Status: this preprint is currently under review for the journal BG.

Short-term response of benthic foraminifera to fine sediment depositional events simulated in microcosm

Corentin Guilhermic, Maria Pia Nardelli, Aurélia Mouret, Damien Le Moigne, and Hélène Howa

Abstract. A microcosm experiment was designed to describe how benthic foraminifera react to fine sediment deposits varying in frequency and intensity, as it may occur regularly or occasionally in coastal benthic environments, caused by discharges from (e.g.) river flooding, tidewater glacier melting in polar regions or diverse anthropic activities linked to harbour or watershed management. The influence of seabed burial resulting from these events on the ecology of benthic ecosystems is often overlooked, and the resilience of benthic communities is poorly known. During a 51-day long experiment, a typical northeastern Atlantic intertidal foraminiferal community, mainly represented by Ammonia confertitesta and Haynesina germanica species, was subjected to two kinds of sedimentary disturbance: 1) one-time high volume (OHV) deposit, i.e. about 3 cm thick sediment added in one time at the beginning of the experiment; and 2) frequent low volume (FLV) deposits, i.e. about 0.5 cm added each week for 4 weeks. The geochemical environment (e.g. dissolved oxygen penetration in the sediment, salinity, temperature and nutrient content in the supernatant water) was monitored to follow the microcosm steady state before and during the experiment. In both disturbed microcosms, H. germanica showed a significant linear decrease in abundance during the experiment while the total abundance of foraminifera was significantly affected only by the OHV treatment, suggesting a stronger effect of a single thick deposit on standing stocks and biodiversity compared to frequent low sediment supplies. Concerning the vertical migration of foraminifera after sedimentary disturbances, the two dominant species moved upwards to the water- sediment interface with migration speeds estimated at 0.41 and 0.47 mm/h respectively for A. confertitesta and H. germanica. In the FLV treatment, the resilient state was already reached within the day following a low thickness burial while in the OHV it was achieved between 1 and 7 days after the 3 cm thick deposit. These results suggest that foraminifera can migrate rapidly after a sedimentary burial to recover their preferential life position under the new sediment-water interface, but in case of an abrupt thick burial, several days are needed to reach a resilient state.

Received: 14 Feb 2023 – Discussion started: 20 Feb 2023

Corentin Guilhermic et al.

Status: open (until 23 Apr 2023)

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RC1:
'Comment on bg-2023-31', Anonymous Referee #1, 12 Mar 2023 reply
Interesting new data about the foraminiferal reaction to seabed burials were presented in the manuscript. In a microcosm experiment containing an intertidal foraminiferal assemblage, the foraminiferal resilience to sediment deposits after a one-time high volume deposit and frequent low volume deposits were observed during seven weeks of incubation. Foraminiferal faunal composition and vertical distribution, as well as geochemical gradients were monitored during the experiment. The topic and the results address relevant scientific questions within the scope of biogeosciences. The manuscript is well written and well organized, the English needs sometimes improvements.
The following points should be addressed by the authors:
Can you give some information about the grain size distribution of the sediments you used?

Concerning total foraminiferal abundances (Fig. 5), I find it difficult to define one out of two counts as outlier point. What about T4 control, here you also have a very high variability between both replicates. I would recommend to include all data points in your analysis.

Do you also treat this T0 Control replicate as an outlier point when comparing the abundances of the two main species?

Some minor points:
The brackets concerning the references do not always seem to be on the correct position. Especially in sentences like in line 71. I suggest adapting it consistently in the manuscript, e.g. in line 71 always put only the year in brackets: “…model from Jorissen et al. (1995)….”
Line 43: Please correct: “… flooding (Extence et al.,…………2015), glacier……..”
Line 54: Please correct: “… considered as one of ….”
Line 89-94: These sentences need language improvements.
Line 102: slikke?
Line 164: The grid was removed after placing the foraminiferal samples, correct?
Fig. 6 and 7: The numbering is twisted.
Fig. 6 (should be 7): Species names must be written in italics.
Line 389: I would cancel the following sentence: “We estimated a maximum speed of 1.4 mm.h-1 for A. confertitesta and for H. germanica." This information is more confusing here than helpful, because both species have different velocities.
Line 467: How fast would these species reach a size of 125 µm after reproduction?
Line 481: The following reference deals with H. germanica food preferences and may be helpful for this discussion here: Wukovits et al., 2021. Phytodetrital quality (C:N ratio) and temperature changes affect C and N cycling of the intertidal mixotrophic foraminifer Haynesina germanica. Aquatic Biology, 30, 119-132. https://doi.org/10.3354/ab00746
Line 526: Please add: “…. (Fig. 8b)…”
Line 539: The following sentence is confusing: “…Indeed, Koho et al. (2018) reported changes is Ammonia confertitesta (genetic type identified by Holzmann and Pawlowski (2000) and renamed Ammonia confertitesta Zheng 1978, by Hayward et al. (2021) ultrastructure as a stress response to oxygen depletion.
Line 545: Pseudopodia can sometimes be very long and maybe reach already oxygenated layers and provide the foram with oxygen before the body will arrive there.
Table 1: You should also add the name you are using in this study for Ammonia: “… Ammonia tepida /confertitesta

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Citation: https://doi.org/10.5194/bg-2023-31-RC1

Corentin Guilhermic et al.

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Short summary

Coastal seas experience sediment discharges which intensity and frequency can strongly be affected by human activities and climate change. We analysed the response of benthic species in an experimental set up. After the burial under a single thick layer of sediment or multiple thin layers at different times, the analysed species migrate rapidly toward the surface. A stronger effect of a single thick deposit on standing stocks and biodiversity is visible compared to frequent low sediment inputs.


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